This invention relates to a waste heat recovery system and to a method of using the same. In particular it relates to a waste heat recovery system for a gas turbine system and to a method for using a heat recovery cycle with the exhaust gases produced by a gas turbine system.
Throughout the world, gas turbines burning a combustable fuel are used to generate power. This power can be used for example to drive fluid pumps, to operate gas compressors, to operate other equipment and to generate electricity. Often these turbines are located in remote places around the globe where there are extreme weather conditions including freezing temperatures. When operating, the gas turbines produce exhaust gases that are usually extremely hot, and just as often, these hot gases are merely exhausted into the atmosphere instead of being utilized to generate additional power.
For example, high pressure natural gas transmission pipelines are conventionally used for transporting gas from production fields to customers remotely located from the fields. Gas compressors feeding such pipelines usually are powered by a gas turbine, and optionally, a heat recovery cycle can be employed to reduce the net power requirements by converting waste heat in the hot exhaust gases from the turbine into electricity. An installation of this type is illustrated in the U.S. Fisher et al. U.S. Pat. No. 5,632,143 issued May 27, 1997 which is incorporated herein by reference. In summary, this patent discloses a combined cycle power plant having a gas turbine system. In one embodiment a bottoming steam turbine power plant utilizes heat contained in the exhaust gases exiting the gas turbine system while in another embodiment a bottoming organic Rankine cycle power plant utilizes heat contained in the exhaust gases of the gas turbine system. Typically, the temperature of the exhaust gases is about 450xc2x0 C. In accordance with this patent the temperature of the gases from which heat is transferred to the bottoming power plant is controlled using ambient air added to the exhaust gases of the gas turbine system. During cold weather, ambient temperatures may drop below freezing causing the steam condensate to freeze thus adversely affecting the operation of the heat recovery system.
On the other hand, organic fluids operating as the working fluid in such systems having relatively high temperatures may not be stable.
There is therefore a need for an improved heat recovery cycle for a gas turbine system which can be utilized in extreme temperature climates, on the one hand, and yet has an improved heat recovery cycle.
The present invention provides a heat recovery system for heat produced by a heat source, such as a gas turbine system. The heat recovery system uses an organic fluid as the working fluid so that the heat recovery system can be used in extreme temperature climates in which temperatures drop below the freezing point for water. In addition, the present invention provides an increased safety factor by utilizing an intermediate fluid to transfer the heat from the hot exhaust gases to the organic working fluid.
In a preferred embodiment of the present invention, four major systems are interconnected. The first system is a gas turbine system in which the gas turbine is a primary motive force for some particular application, such as driving a gas compressor remotely located geographically and used in a natural gas line. The gas turbine system generates large amounts of heat that usually is lost to the atmosphere by way of the gas exhaust stacks. The second system is a waste heat recovery system that takes turbine exhaust gas and diverts it from the exhaust stacks to extract heat contained therein and thus extract energy from that which was previously wasted. The third system is an intermediate fluid system which in a preferred embodiment is a pressurized water system and to which the waste heat removed from the turbine exhaust gas is transferred. The fourth system is an organic working fluid system to which the heat from the intermediate fluid is transferred to generate an organic fluid vapor that is used to drive an organic fluid turbine for producing power preferably by using an electric generator connected to the organic fluid turbine.
The present invention thus comprises a waste heat recovery system that transfers heat from a primary heat source, such as heat from the exhaust of a gas turbine, to an intermediate fluid, an intermediate fluid system that transfers the heat to an organic working fluid to generate a vapor, and an organic working fluid system whose vapor operates an organic turbine to generate further power from the waste heat.